Hand-off between ultra-wideband cell sites

ABSTRACT

Briefly, the present invention provides a dynamic channel re-assignment capability between mobile units, base stations and sectors within base station coverage areas. The wireless devices used in the present invention may include ultra-wideband radio communication devices. Ultra-wideband bandwidth and channel allocation can be effectively managed, even though link quality generally deteriorates near the outer boundary of the base station. By maintaining dual communications with an adjoining base station, the present invention reduces the bit error rate and maintains signal strength.

This application is a divisional of, and claims priority from, U.S.non-provisional application Ser. No. 09/804,110, filed Mar. 12, 2001,entitled: “HANDOFF BETWEEN ULTRA-WIDEBAND CELL SITES,” which claimspriority from U.S. provisional patent application Ser. No. 60/255,469,filed Dec. 14, 2000, and entitled “Ultra-Wideband Communication Systemand Method”, which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to the field of ultra-widebandcommunication systems. More particularly, the present invention relatesto hand-offs between cell sites in an ultra-wideband communicationsystem.

BACKGROUND OF THE INVENTION

Wireless communication systems are changing the way people work,entertain, and communicate. For example, portable phones and othermobile devices have enabled highly mobile individuals to easilycommunicate. Such devices can transmit and receive both voice and datasignals. As more features are added to these mobile wireless devices,users are able to receive a wider variety of information. This enhancesthe user's entertainment and more efficiently solves the user's businessproblems.

Data, such as computer files, graphics, video, and music may be sentfrom a remote location and received by mobile wireless devices locatedthroughout a large (or “wide”) area. Such wide area uses generallyrequire a series of fixed transceivers arranged to communicate with themobile wireless devices. The wireless device is able to communicate onlyas long as it remains in contact with at least one of the transceivers.

While the use of such wide area systems is expanding, the use of localwireless communication systems is also growing. A local wirelesscommunication system, for example, may configure the wireless devices ina single building, such as a residence, to share information. Such localwireless communication systems may enable computers to controlperipherals without physical connections, stereo components tocommunicate, and almost any appliance to send and receive information tothe Internet.

The amount of data being sent on both wide area and local communicationsystems is mushrooming, and it may quickly exceed the bandwidthavailable in the traditional communication bands. A relatively newcommunication technology (termed “ultra-wideband” technology) mayprovide assistance in meeting the ever-increasing bandwidth demands. Anexample of ultra-wideband technology is the communication system usingan impulse radio system that is disclosed in U.S. Pat. No. 6,031,862,entitled “Ultra-Wideband Communication System and Method”. Impulse radiouses individually pulsed monocycles emitted at fractions of nanosecondintervals to transmit a digital signal. For many applications, thepulses are transmitted at extremely low power density levels, forexample, at less than −30 dB. The generated pulses are so small thatthey typically exist in the noise floor of other more traditionalcommunication systems.

Ultra-Wide band communication systems enable communication at a veryhigh data rate, such as 100 megabits per second or greater, whenoperated in a small local area. Ultra-Wideband systems, however, mustoperate at extremely low power, typically transmitting signals at thenoise level. These systems must operate at low power because they needto avoid interfering with the more established communicationfrequencies. The low power requirement restricts the size of eachultra-wideband cell Thus, ultra-wideband cells generally are smallerthan the cells in the more traditional continuous wave or carrier basedsystems.

The relatively small size of a cell in an ultra-wideband communicationsystem necessitates a relatively dense placement of base stationantennas. This high density of antennas may, under some circumstances,lead to cross-talk between the channels assigned to different users.This is especially true if the users are highly mobile. In this case,they will often travel across cell boundaries where the signals of twoor more base stations overlap. Since this event will be relativelyfrequent with such small cells, user channels must be geographicallyseparated to minimize the occurrence of channel interference. Forexample, if a particular channel is used in a cell, that channel shouldnot be used in any other cell within several miles. Accordingly, sinceonly relatively few of the communication channels can be allocated toeach cell, the reuse distance determines the total capacity of theoverall cell communication system.

The utilized bandwidth in conventional cells varies as a function ofuser demand. Since user demand can vary greatly from one time period toanother, there are likely to be times when a particular cell is greatlyunder-utilized. There are also likely to be other times when that samecell is saturated, thereby causing undesirable drops in transmissions,connection refusals, and quality degradation. When a cell's bandwidthutilization exceeds system quality standards in a conventionalcommunication system, the system operator typically will add anothercell in the area to move some of the user traffic from the over-utilizedcell to the new cell. Adding cells and antennas, however, can be acostly and time-consuming process.

Although ultra-wideband technology has the ability to decrease theimpact of multipath interference, it is still subject to attenuation ofthe received signal as the signal passes between transmitter andreceiver. For a point RF source, received signal strength varies as theinverse of the squared distance for open line of sight communications.In cluttered and mobile environments, the attenuation is more closelyproportional to the inverse of the fourth power of the distance. This isdue to multipath cancellation, which is present even in ultra-widebandsignals. In either scenario, the attenuation of the signal can decreasethe signal level to a value that is unsuitable for reliable datatransfer.

Due in part to the deficiencies described above, conventionalultra-wideband communication systems risk poor quality of service,especially as a mobile unit moves from one location to another. Suchsystems also do not enable entirely efficient utilization of bandwidthand system resources.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide mobileultra-wideband methods and devices for effectively linking andmaintaining an acceptable level of service and coverage whilesimultaneously handling multiple data streams and multiple users. It isalso an object of the present invention to efficiently utilize bandwidthand system resources. To meet the stated objectives, and to overcome orgreatly alleviate the disadvantages in known ultra-wideband units, thepresent invention provides methods, systems, software and relateddevices for performing a “soft hand-off” between and withinultra-wideband cells.

Briefly, the present invention provides a dynamic channel re-assignmentcapability to mobile units, base stations and sectors within basestation coverage areas. The wireless devices may include impulse radiocommunication devices such as ultra-wideband radio (also known asdigital pulse wireless) communication devices. The bandwidth and channelallocation of these devices and sectors can be effectively managed withthe present invention despite the fact that link quality generallydeteriorates near the outer boundary of the base station. This effectivemanagement is achieved by having the mobile unit maintain dualcommunication with a linked base station and an adjoining base station.The present invention thereby reduces the bit error rate and maintainssignal strength (e.g., RF signal strength). This dual communicationprocedure is termed a “soft-handoff\

In the present invention the mobile units and base stations constantlymonitor both signal strength and the bit error rate in order todetermine whether there is a need for a hand-off. When the dataintegrity of a mobile unit drops below a minimum acceptable bit errorrate (BER), and/or the signal strength drops below a pre-determinedminimum acceptable level, a soft hand-off that maintains acceptableservice will be initiated. FIG. 1 lists the typical minimum acceptablebit error rates for video, audio and data.

Advantageously, the present invention efficiently insures that a softhand-off is performed for a mobile device as it moves from one locationto another. This greatly enhances the desirability of the associatedultra-wide band system by minimizing or eliminating interruptions incommunication. High quality communication is thus maintained and at thesame time the ability to accommodate additional traffic is provided.

In one aspect the present invention features a method for performing asoft hand-off in a cellular communication system (preferably acode-based cellular communication system) and a corresponding computerprogram product. The method involves the steps of: (a) monitoring signalstrength and the bit error rate from a primary source (preferably anultra-wideband primary source); (b) monitoring signal strength and thebit error rate from a secondary source (preferably an ultra-widebandsecondary source); (c) comparing the strength of the signal and the biterror rate from the primary source to the strength of the signal and thebit error rate from the secondary source; and (d) transferring datareception and transmission from the primary source to the secondarysource when the strength of the signal from the secondary source isgreater than the strength of the signal of the primary source, or whenthe bit error rate of the secondary source is less than the bit errorrate of the primary source, or when either signal strength or bit errorrate is below a pre-determined level. Monitoring signal strength mayinvolve determining signal strength and storing the information inmemory.

In one embodiment, the hand-off is from a first base station to a secondbase station to a mobile unit. In this case: (a) the first base stationis linked to the mobile unit and selects an adjoining second basestation; (b) the first base station contacts the second base station torequest initial hand-off sequence; (c) the second base stationacknowledges the request, provides a channel assignment to the mobileunit and links to the mobile unit; (d) the mobile unit transmits ahand-off release to the first base station; and (e) the first basestation releases the mobile unit and completes the soft hand-off.

In another embodiment, the soft hand-off is from a mobile unit to afirst base station to a second base station. In this case: (a) themobile unit is linked to the first base station and detects an increasein bit error rate and/or a reduction in signal strength; (b) the mobileunit sends a request to the first base station for a hand-off; (c) thefirst base station receives the request, selects the second base stationand contacts the second base station to request an initial hand-offsequence; (d) the second base station acknowledges the request for aninitial hand-off sequence; (e) the second base station contacts themobile unit, provides a channel assignment to the mobile unit and linksto the mobile unit; (f) the mobile unit transmits a hand-off releaserequest to the first base station; and (g) the first base stationreleases the mobile unit, and thereby completes the soft hand-off.

In still another embodiment, the soft hand-off involves dynamic powerrange linking. In this embodiment: (a) a mobile device is linked to afirst base station and requests the position of a plurality of basestations; (b) the plurality of base stations reply; (c) the mobile unitdetermines and stores the location of each of the base stations; (d)each of the base stations transmits an associated rating to the mobiledevice; (e) the mobile device calculates the data integrity of each basestation and establishes a link with a base station having the highestdata integrity; and (f) the mobile device transmits a link curtailmentto the first base station.

In another aspect, the invention provides a method for performing a softhand-off in a code-based cellular communication system. The softhand-off is from a first mobile unit to a second mobile unit to a basestation. The method involves the steps of: (a) monitoring signalstrength and the bit error rate from a first base station anddetermining that either in unacceptable; (b) attempting to locate anadjacent base station with an acceptable signal strength and bit errorrate and determining that no adjacent base station has an acceptablesignal strength and bit error rate; (c) transmitting a hand-off requestfrom a first mobile device that is linked to the first base station to asecond mobile device; (d) receiving a response from the second mobiledevice; and (e) using the second mobile device as a temporary repeaterto pass data to a second base station.

In yet another aspect, the present invention provides an adaptive linkcontroller. The adaptive link controller includes: (a) logic formonitoring the signal strength and bit error rate of a mobile unit and aplurality of base stations; (b) logic for performing dual linkcoordination and maintenance with a linked base station and a hand-offbase station; and (c) logic for performing hand-off initiation and linkcurtailment.

For each of the methods of the invention described above, acorresponding computer program product is also provided. The inventionalso features ultra-wideband code based cellular communications systemscapable of performing each of the methods of the invention. The presentinvention also features mobile units and base stations that areconfigured and structured to operate in such systems.

BRIEF DESCRIPTION OF THE DRAWINGS

The nature, goals, and advantages of the invention will become moreapparent to those skilled in the art after considering the followingdetailed description when read in connection with the accompanyingdrawing in which like reference numerals identify like elementsthroughout, wherein:

FIG. 1 lists typical minimum acceptable bit error rates for video, audioand data in accordance with the present invention;

FIG. 2 shows base station architecture with overlapping coverage inaccordance with the present invention;

FIG. 3 shows a single base station with connectivity to six other basestations for handoff and channel coordination in accordance with thepresent invention;

FIG. 4 shows sectorization at an ultra-wide band base station inaccordance with the present invention;

FIG. 5 is a flowchart for scenario one (a soft hand-off from basestation to new base station to mobile unit) in accordance with thepresent invention;

FIG. 6 is a flowchart for scenario two (a soft hand-off from mobile unitto base station to new base station) in accordance with the presentinvention;

FIG. 7 is a flowchart for soft handoff scenario number three thatperforms dynamic power range linking in accordance with the presentinvention;

FIG. 8 is a power range linking model for soft handoff with a mobileunit leaving the coverage of base station 2 in accordance with thepresent invention;

FIG. 9 shows scenario four (a soft hand-off from mobile unit to mobileunit to base station with emergency geo-locating) in accordance with thepresent invention;

FIG. 10 is a flow chart for soft hand-off procedures for scenarios onethrough four in accordance with, the present invention; and

FIG. 11 depicts an adaptive link controller in accordance with thepresent invention.

It will be recognized that some or all of the figures may be schematicrepresentations for purposes of illustration and do not necessarilydepict the actual relative sizes or locations of the elements shown.

DETAILED DESCRIPTION OF THE INVENTION

In the following paragraphs, the present inventions will be described indetail by way of example with reference to the attached drawings.Throughout this description, the preferred embodiment and examples shownshould be considered as exemplars, rather than as limitations on thepresent invention. As used herein, “the present invention” refers to anyone of the embodiments of the invention described herein.

I. Soft Hand-Off and Mobile Ultra-Wideband Dynamic Linking Architecture

FIG. 2 illustrates a preferred base station 10 hexagonal topology 100that will provide overlapping coverage 30 for ultra-wideband basestations 10. Other configurations may also be used, such as a micropico-network on a daisy chain backbone, placed like emergency call boxesalong a highway, for separate routing of signals, but this configurationwill allow an effective soft hand-off, which is essential for code-basedcellular communications. Base station topologies can be hexagonal orlinear. The hexagonal topology covers disperse user density environmentswhereas the linear topology mainly covers linear features such as roads.The concept is the same but the number of sectors per base stationdiffers. Given this preferred arrangement, or other suitablearrangements, the present invention may be used in conjunction with themethods, devices, and systems described in U.S. patent application,number to be assigned, entitled “Ultra Wideband Communication System AndMethod”, filed Dec. 13, 2000, which is incorporated herein by referencein its entirety.

The overall base station 10 architecture 100 includes a plurality ofbase stations 10. Each base station 10 has an associated coverage area20, for example a substantially circular coverage area 20 as shown inFIG. 2. The coverage areas 20 of adjacent base stations 10 may overlap,thereby creating overlapping coverage areas 30. The spacing andconfiguration of the base stations 10 and the size and shape of thecoverage areas 20 will determine the size and shape of the overlappingcoverage areas 30. In the hexagonal configuration shown in FIG. 2, eachbase station 10 on the interior of the architecture 100 has six adjacentbase stations 10, while each base station 10 on the exterior of thearchitecture 100 has three adjacent base stations 10.

FIG. 3 shows a single base station 10 with connectivity 40 to six otheradjoining base stations 10. The station in the center 60 links with theother base stations 10 to coordinate allocated channels so thatadjoining base station 10 sectors 50 do not use the same channels. Thesuitability of the channels may be managed using the methods and devicesdescribed in U.S. patent application Ser. No. 09/746,348 entitled“System for Pre-testing and Certification of Multiple Access Codes,”filed Dec. 21, 2000, which is incorporated herein by reference in itsentirety.

The linked architecture 200 also provides an inter-connectedcommunications system that is necessary to provide a “soft hand-off” asa mobile unit 70 moves from the coverage area of one base station 10 tothe coverage area of another. Mobile unit 70 may be a handheld-typemobile device. Alternatively, it may be an ultra-wideband component in amobile phone, a mobile internet device, a portable radio, a personaldata assistant, a desktop computer or appliance located in a home, anautomobile, or office environment or a device for similar applications.

During the “soft hand-off,” the mobile unit 70 will maintain a link withboth base stations 10 until the hand-off is complete. FIG. 3 alsodemonstrates the “sectorization” within the coverage area 20 of the basestation 10. Each base station 10 is sub-divided into six coveragesectors 50. The sub-division provides greater bandwidth management inthe base station's coverage area 20.

FIG. 4 demonstrates that when a mobile unit 70 passes from one sector 50to another 80 within the coverage area 20 of a single base station 10,the base station 10 will complete a “soft hand-off as channelre-assignment is accomplished. In this case, the base station 10 willallocate a new channel for the mobile unit 70 as it moves into anothersector 80, and will maintain the current allocated channel until thehand-off is complete.

II. Soft Hand-Off Scenarios

A. Scenario #1: Base Station to Receiving Base Station to Mobile Unit

FIG. 5 illustrates a preferred soft hand-off technique 500. In step 510,a base station 10 detects an increase in bit error rate and/or areduction in signal strength (e.g., RF signal strength) using knownmethods. The base station 10 that is linked to the mobile unit 70monitors the bit error rate and signal strength between all of it'slinked mobile units 70, as well as their relative geo-locations. Whenthe bit error rate exceeds the acceptable bit error rate limit or thesignal strength drops below the predetermined acceptable level, the basestation 10 initiates the hand-off with an adjoining base station 10. Thehand-off procedure begins with the linked base station 10 selecting themost suitable adjoining base station 10. This selection is based on thecalculated relative geo-positional data (obtained using known methods oras described herein) that the currently linked base station 10 has forthe mobile unit 70 in relation to the best suited base station 10 withinthe hexagonal coverage scheme.

In step 520 the currently linked base station 10 (base station 810)contacts the selected adjoining base station 10 (base station 820) torequest an initial hand-off sequence. Step 530 determines if the firstadjoining base station 10 has replied using known methods. If not, thenin step 540 base station 810 contacts the next available base station 10in the hexagonal coverage scheme. Alternatively, if the first adjoiningbase station 10, here base station 820, has replied, then the initialhand-off sequence is given by base station 820 in step 550. This initialhand-off sequence consists of the acknowledgment to base station 810 forrequested hand-off, the channel assignment selection for the mobile unit70 and the initial contact with the mobile unit 70 by base station 820.At this time the mobile unit 70 is in communication with both basestation 810 and base station 820.

After base station 820 links with the requesting mobile unit 70 in step560 and both calculate and “acceptable” bit error rate and signalstrength, the mobile unit 70 will transmit in step 570 a hand-offrelease request to base station 810. In step 580, base station 810 thenreleases the mobile unit 70, and in step 590 the soft hand-off iscomplete.

B. Scenario #2: Initiation by Mobile Unit in Contact with Base Station

FIG. 6 illustrates that when a mobile ultra-wideband unit 70 moves fromone coverage area 20 to another, the hand-off process happens inmultiple steps. FIG. 6 illustrates the process 600 when a base station10 or mobile unit 70 detects, in step 620, an increase in bit error rateand/or a reduction in signal strength. In step 630, the mobile unit 70initiates the hand-off request to the linked base station 810 if themobile unit 70 detects the quality of service changes. When the biterror rate has exceeded the acceptable limit (e.g., see FIG. 1) or thesignal strength drops below the predetermined acceptable level, themobile unit 70 sends a request in step 640 to the linked base station 10for a hand-off to an adjoining base station 10.

After the linked base station 10 has received the request, the hand-offprocedure starts with the linked base station 10 selecting the mostsuitable adjoining base station 10. This selection is based on the basestation 10 sector 50 occupied by the mobile user or, as in step 650, theknown geo-location of the mobile unit 70 in relation to the best suitedbase station 10 within the hexagonal coverage scheme. Thus, at this timethe base station 10 has, from step 650, an up-to-date geo-location onthe mobile unit 70, and the six nearest neighbor base stations 10.

In step 640, the currently linked base station 10 (base station 810)contacts the selected adjoining base station 10 (base station 820) thatit predicts to be within range of the mobile unit 70 (based on themobile's position and direction) to request an initial hand-offsequence. Step 660 determines if the new base station 10 is able to takethe mobile unit 70. If not, then in step 665 base station 810 contactsthe next closest base station 10 in the hexagonal coverage scheme.

If base station 820 can accept the mobile unit 70, it sends anacknowledgement in step 670 to base station 810 and proceeds to linkwith the mobile unit 70. In step 670, the initial hand-off sequence bybase station 820 includes the acknowledgment to base station 810 forrequested hand-off, the channel assignment selection for the mobile unit70 and the initial contact with the mobile unit 70 by base station 820.At this time the mobile unit 70 is data linked to both base station 810and base station 820. The mobile unit 70 will remain linked to basestation 810 until a confirmed Quality of Service (QOS) link with basestation 820 or another base station 10 is established.

After base station 820 links with the requesting mobile unit 70, adialogue ensues that leads to a calculation of a bit error rate andsignal strength. If this bit error rate and signal strength are belterthan that achieved through base station 810, as determined in step 675,then, in step 680 base station 820 will link with the mobile unit 70 andestablish a data channel. Then, the mobile unit 70 will, in step 685,transmit a hand-off release request to base station 810. Base station810 then releases the mobile unit 70 in step 690, and, as shown in step695, the soft hand-off is complete.

B. Scenario #3: Mobile Ultra-Wideband Dynamic Power Range Linking

FIG. 7 demonstrates the principles of the ultra-wideband dynamic powerrange linking and soft hand-off technique 700. In this technique amobile ultra-wideband unit 70 can determine and select a base station 10that will provide optimum signal integrity. The process includes notonly the initial “handshake” with the base station 10 providing themobile unit 70 with optimum capability, but also provides a coordinated“soft hand-off” as required with the previously linked base station 10.

In step 710 a mobile device 70 is linked to a first base station 10 andrequests the position of a plurality of base stations 10. In steps 715and 725 it is determined if the plurality of base stations 10 reply.Once the plurality of base stations 10 reply, then in steps 730 an! 735the mobile unit 70 determines and stores the location of each of thebase stations 10. The determination of the location may be done byconventional triangulation or it may be done using the methods and/ordevices described in U.S. patent application Ser. No. 09/745,498,entitled “Use of Third-Party Ultra-Wideband Devices to EstablishGeo-Positional Data,” filed Dec. 22, 2000, which is incorporated hereinby reference in its entirety.

In steps 740 and 745 the projected bit error rate (PBER) algorithms areperformed. In steps 750 and 755 each of the base stations 10 transmitsan associated rating to the mobile device 70. In step 760 the mobiledevice 70 calculates the data integrity of each base station 10 andestablishes a link with a base station 10 having the highest dataintegrity. In step 770 the mobile device 70 transmits a link curtailmentto the fiistbase station 1.0.

This process is accomplished in a fashion that is transparent to themobile user. FIG. 8 illustrates a mobile ultra-wideband device 70 thatis within transmission range of two ultra-wide band towers 810 and 820and is in a location that would benefit from a hand-off. In thisdiagram, the transmission distance to base station 810 is a₁, and thetransmission distance to base station 820 is b₁. The mobileultra-wideband device 70 will require less power (e.g., RF power) totransmit to base station 820 at distance b₁ than to base station 810 atdistance a₁.

The present invention additionally manages system bandwidth byrestricting power level such as RF power levels, in mobileultra-wideband devices 70 to the smallest amount necessary to maintain adata link with an acceptable level of service. In FIG. 8, the limited RFpower output would keep the mobile unit 70 primarily within thebroadcast range of base station 820. Since the mobile ultra-widebanddevice's transmission is limited to base station 820, only bandwidthfrom base station 820 is utilized and no adjoining base station'sbandwidth is encumbered. As the mobile ultra-wideband 70 moves away fromthe base station 10, the bit error rate will increase and the signalstrength will drop to the predetermined point where data is unacceptableand a soft hand-off will be initiated. Power level can be furtherminimized by combining the present invention with the technologydescribed in U.S. patent application Ser. No. 09/677,082, entitled“Communication System”, filed Sep. 29, 2000, which is incorporatedherein by reference in its entirety.

C. Scenario #4: Mobile Unit to Mobile Unit to Base Station

FIG. 9 illustrates the process when a mobile unit 70 detects an increasein bit error rate and/or a reduction in RF signal strength. The mobileunit 70 also has been unable to contact another base station 10 directlyand the currently linked base station 10 (base station two (820) in thiscase) is unable to initiate a hand-off routine to another adjoining basestation 10. In this case the mobile unit 70 (mobile unit two (920))initiates the “mobile unit to mobile unit link hand-off request” to anymobile unit 70 that will respond. The mobile unit 70 that responds tothis request (mobile unit one (910)) will then perform, as a temporaryrepeater to pass mobile unit 2 (920) geo-location data to base stationone (810). This may be useful, for example, for emergency 911 linking.

III. Hand-off Procedure Cycle

FIG. 10 shows the procedural flow 1000 for conducting a soft hand-off.This shows the four scenarios and the situations in which they would beconducted. When the bit error rate or the signal strength has reachedthe level where the quality of service is no longer acceptable, the basestation 10 or the mobile unit 70 will initiate the procedures for ahand-off to an adjoining base station 10. Due to various fieldconditions, both the base station 10 and the mobile unit 70 have theindividual capability to “request” a hand-off to another base station 10to maintain quality of service. In the event that a mobile unit 70cannot contact a base station 10, including the previous linked basestation 10, the mobile unit 70 will conduct a “Tower Range Linking”procedure. This procedure will locate and link with a neighboring mobileunit 70 for the purpose of using the contacted mobile unit 70 as atemporary repeater and as an emergency “911” link back to a base station10.

The overall scheme 1000 begins in step 1010 when the mobile unit 70 linkto base station 10 degrades, either due to an increased bit error rateor a signal decrease. In step 1020 it is determined, whether the basestation 10 detects the degraded link. If yes, then the hand-offprocedures are initiated in step 1040. If no, then in step 1030 themobile unit 70 detects the degraded link.

Then, in step 1050, it is determined whether the mobile unit 70 hassuccessfully conducted a soft hand-off through the linked base station10. If yes, then the hand-off procedures arc initiated in step 1040. Ifno, then in step 1060, the mobile unit 70 initiates power range linking.

In step 1070 it is determined whether the mobile unit 70 has conducted asoft hand-off through, power range linking. If yes, then the hand-offprocedures are initiated in step 1040. If no, then the mobile unit 70initiates power range linking with the nearest mobile unit 70 for anemergency repeater link to a base station 10.

IV. Adaptive Link Controller

An adaptive link controller (ALC) is structured to provide at least oneof the following acts at a mobile unit, a base station or somecombination thereof: (a) constantly monitoring the Bit Error Rate (BER);(b) after reaching a predetermined threshold, searching active cells fora link with a greater signal strength based on a minimum acceptablelevel; (c) monitoring signal strengths of other signals within the cell;(d) maintaining a two-way link between base stations and mobile units inhand-off process; (e) performing hand-off request and hand-off actions;(f) performing emergency link management; (g) creating emergency messageset; (h) performing an overall data link coordination; and/or (i)performing vector manipulation beam tracking.

Thus, for example, the ALC may provide the hand-off coordination andexecution. As indicated in steps 1110 and 1120, the adaptive linkcontroller monitors the bit error rate and the overall “quality ofservice” in both the mobile ultra-wideband unit 70 and the base stations10. When the channel quality has dropped below acceptable level and thequality of service is diminished, the adaptive link controller in eitherthe base station 10 or the mobile unit 70 performs the steps necessaryto conduct a hand-off.

FIG. 11 illustrates how the adaptive link controller monitors thechannel quality with the assigned mobile units 70 and the adjoining basestations 10, As a mobile unit 70 traverses through, the coverage area 20of a base station 10, the mobile unit's adaptive link controllermaintains the status of the link with the base station 10. Additionally,in step 1130 the base station 10 adaptive link controller monitors thelink status of the mobile units 70 in its coverage area 20, as well asthe “local” adjoining base stations 10 that would be us ed for hand-off.The adaptive link controller provides and maintains a dual link (i.e.,the mobile unit 70 is in communications with two base stations 10 on twoseparate channels) during the hand-off process. In step 1140 theadaptive link controller initiates a link curtailment after the hand-offhas effectively transferred control to the receiving base station 10.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of a preferred embodiment shouldnot be limited by any of the above-described exemplary embodiments, butshould be defined only in accordance with the following claims and theirequivalents.

1. A method for performing a soft hand-off in an ultra-widebandcode-based cellular communication system, wherein the soft hand-off isfrom a first mobile unit to a second mobile unit to a base station, themethod comprising the steps of: monitoring signal strength and the biterror rate from a first base station and determining that either isunacceptable; attempting to locate an adjacent base station with anacceptable signal strength and bit error rate and determining that noadjacent base station has an acceptable signal strength and bit errorrate; transmitting a hand-off request from a first mobile device that islinked to the first base station to a second mobile device: receiving; aresponse from the second mobile device: and using the second mobiledevice as a temporary repeater to pass data to a second base station. 2.A computer program product for performing a soft hand-off in anultra-wideband code-based cellular communication system, wherein thesoft hand-off is from a first mobile unit to a second mobile unit to abase station, comprising: computer code for monitoring signal strengthand the bit error rate from a first base station and determining thateither in unacceptable; computer code for attempting to locate anadjacent base station with an acceptable signal strength and bit errorrate and determining that no adjacent base station has an acceptablesignal strength and bit error rate; computer code for transmitting ahand-off request from a first mobile device that is linked to the firstbase station to a second mobile device; computer code for receiving aresponse from the second mobile device; and computer code for using thesecond mobile device as a temporary repeater to pass data to a secondbase station.
 3. A system for performing a soft hand-off in anultra-wideband code-based cellular communication system, wherein thesoft hand-off is from a first mobile unit to a second mobile unit to abase station, the system comprising: means for monitoring signalstrength and the bit error rate from a first base station anddetermining that either is unacceptable; means for attempting to locatean adjacent base station with an acceptable signal strength and hiterror rate and determining that no adjacent base station has anacceptable signal strength and bit error rate; means for transmitting ahand-off request from a first mobile device that is linked to the firstbase station to a second mobile device; means for receiving a responsefrom the second mobile device; and means for using the second mobiledevice as a temporary repeater to pass data to a second base station. 4.A mobile unit for an ultra-wideband code-based cellular communicationsystem, wherein mobile unit performs a soft hand-off to a second mobileunit to a base station, the mobile unit comprising: means for monitoringsignal strength and the bit error rate from a first base station towhich it is linked sod determining that either is unacceptable; meansfor attempting to locate an adjacent base station with an acceptablesignal strength and bit error rate and determining that no adjacent basestation has an acceptable signal strength and bit error rate; means fortransmitting a hand-off request to a second mobile device; means forreceiving a response from the second mobile device; and means for usingthe second mobile device as a temporary repeater to pass data to asecond base station.
 5. A base station system for an ultra-widebandcode-based cellular communication system, wherein there is a softhand-off from a first mobile unit to a second mobile unit to the basestation, the base station comprising: means for monitoring signalstrength and the bit error rate from the first base station anddetermining that either is unacceptable; and means for attempting tolocate an adjacent base station with an acceptable signal strength andbit error rate and determining that no adjacent base station has anacceptable signal strength and bit error rate.